base: Cleanup class/struct forward declarations

base/android/java_message_handler_factory.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_ANDROID_JAVA_MESSAGE_HANDLER_FACTORY_H_
 #define BASE_ANDROID_JAVA_MESSAGE_HANDLER_FACTORY_H_
 
 #include "base/android/scoped_java_ref.h"
 #include "base/message_loop/message_pump.h"
 
 namespace base {
 
 class MessagePumpForUI;
+class WaitableEvent;
 
 namespace android {
 
 // Factory for creating the Java-side system message handler - only used for
 // testing.
 class JavaMessageHandlerFactory {
  public:
   virtual ~JavaMessageHandlerFactory() {}
   virtual base::android::ScopedJavaLocalRef<jobject> CreateMessageHandler(
       JNIEnv* env,
       base::MessagePump::Delegate* delegate,
       MessagePumpForUI* message_pump,
       WaitableEvent* test_done_event) = 0;
 };
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_JAVA_MESSAGE_HANDLER_FACTORY_H_